FIG. 14 shows a block diagram illustrating a conventional high-frequency receiver. In FIG. 14, input terminal 1 receives high-frequency signals having frequencies ranging from 55.25 MHz to 801.25 MHz. Input terminal 1 connects to single-tuned filter 2 of which tuned frequency ranges from 367.25 MHz to 801.25 MHz (UHF broadcasting band). The tuned frequency is controlled by a tuning voltage supplied to frequency variable terminal 2a. 
High-frequency amplifier 3 receives an output signal from single-tuned filter 2, amplifies signals of UHF band, and outputs the resultant signals to double-tuned filer 4. Filter 4 includes two variable capacitance diodes, and tuned frequencies are controlled by a tuning voltage supplied to frequency variable terminal 4a. 
Mixer 5 receives an output signal from double-tuned filter 4 at its first input terminal 5f, and receives an output signal from local oscillator 6 at its second input terminal 5s via frequency divider 7. Mixer 5 mixes UHF band signals having undergone double-tuned filter 4 with oscillating signals supplied from local oscillator 6, and converts the resultant signals into intermediate frequency signals of 45.75 MHz.
Intermediate frequency filter 8 connects to an output terminal of mixer 5, and attenuates undesired signals in occupied frequency bandwidth of 6 MHz. Output signals from intermediate frequency filter 8 is supplied to output terminal 9 via intermediate frequency amplifier 25.
UHF signal receiving section 10 is thus formed of single-tuned filter 2, high-frequency amplifier 3, double-tuned filter 4, mixer 5 and intermediate frequency filter 8.
The high frequency signal supplied to input terminal 1 is also supplied to VHF signal receiving section 11, which receives signals having frequencies ranging from 55.25 MHz to 361.25 MHz (VHF broadcasting band). VHF signal receiving section 11 is formed of single-tune filter 12, high-frequency amplifier 13, double-tuned filter 14 and mixer 15.
Single-tuned filer 12 includes one variable capacitance diode, and its tuned frequency is controlled by a tuning voltage supplied to frequency variable terminal 12a. High-frequency amplifier 13 connects to an output terminal of single-tuned filter 12, and amplifies VHF band signals. Double-tuned filter 14 connects to an output terminal of high-frequency amplifier 13, and it has two variable capacitance diodes. Its tuned frequency is controlled by a tuning voltage supplied to frequency variable terminal 14a. 
Image rejection mixer (IRM) 15 is formed of two mixers and two phase shifters. IRM 15 receives an output signal from double-tuned filter 14 at its first input terminal 15f, and receives an output signal from local oscillator 6 via frequency divider 16 at its second input terminal 15s. IRM 15 mixes the VHF band signals having undergone double-tuned filter 14 with oscillating signals supplied from local oscillator 6, and converts the mixed signals into signals having intermediate frequency of 45.75 MHz. IRM 15 supplies the resultant signals to intermediate filter 8 via lead-wire 26.
Local oscillator 6 includes OSC 17 of which input terminals 17a and 17b are connected to tuning section 18. Tuning section 18 is formed of series-connected unit 21 formed of variable capacitance diode 19 and capacitor 20 connected in series, and inductor 22 connected in parallel with unit 21.
Phase locked loop (PLL) circuit 23 placed approx. at the center of FIG. 14 receives output signals from OSC 17 at its input terminal, and supplies a tuning voltage from its output terminal 23a to variable capacitance diode 19 of tuning section 18. The tuning voltage is also supplied to respective variable capacitance diodes of single-tuned filter 2, double-tuned filter 4, single-tuned filter 12, and double-tuned filter 14. The tuning voltage thus controls oscillating frequency of local oscillator 6 as well as respective tuned frequencies of single-tuned filters 2, 12, double-tuned filters 4, 14.
Meanwhile, the prior art related to the present invention are disclosed, e.g. in Japanese Patent Unexamined Publication No. 2000-295539, 2002-118795, and H01-265688.
The conventional high-frequency receiver discussed above; however, must include two mixers and two phase shifters regardless of whether or not they receive signals having frequencies interfering with images in a received channel. Thus the receivers are required to consume less power, and it is hard particularly for battery-operated portable devices to achieve this requirement.
The present invention thus aims to provide high-frequency receivers consuming less power and portable devices using the same receivers.